1. Technical Field
This invention relates to a hierarchical representation of a state diagram. More specifically, the invention relates to graphically presenting modifications to the hierarchical state diagram in a manner that transfers across the hierarchical layers therein.
2. Description of the Prior Art
State diagrams are used to graphically represent finite state machines. One form of a state diagram for a finite state machine is a directed graph. Another form of the state diagram is represented through the unified modeling language (UML), i.e. a modeling language in which the state diagram includes standardized notation that can describe computer programs, business processes, etc. Basic notational elements that make up a diagram include the following: a filled circle pointing to the initial state, a hollow circle containing a smaller filled circle indicating the final state, a rounded rectangle denoting a state, an arrow denoting transition, and one or more horizontal lines denoting a join or a fork. UML state machine diagrams depict the various states that an object may be in and the transitions between those states. In the state diagram, a state represents a stage in the behavior of an object, including an initial state, a final state, and possibly transition states. An initial state, also known as a creation state, is one that an object is in when it is first created. In contrast, a final state is one in which no transactions lead out of. A transition state is a state between the initial state and the final state, and is a state that represents a progression from one state to another. The transition state is triggered by an event that is either internal or external to the object. Accordingly, the state diagram models objects that exhibits both behavior and state.
In a conventional state diagram, all states are represented at the same level. The design does not capture the commonality that exists among states. A hierarchical state machine diagram captures the commonality by organizing the states as a hierarchy. The states at the higher level in the hierarchy perform common message handling, while the lower level states inherit the commonality from the higher level states and perform state specific functions.
State diagrams are stored according to internal data transcription. It is known in the art that state diagrams may be modified over time. However, because the diagram is stored according to internal data transcription, it is difficult to understand the difference between a second version diagram and the original diagram. The difficulties understanding modification of the models increases with complexity with respect to the hierarchical state diagram wherein the differences may need to be expressed at different levels in the hierarchy.
Therefore there is a need to facilitate presentation and viewing of modifications of a hierarchical state diagram. The review process should be limited to a specific level in the hierarchy in order to mitigate the complexity of the comparison process across the levels of the hierarchy.